Filling in door lock holes

I live in a historical area so I can't just go out and buy a new door without approval. That being said, I wanted to swap out the door hardware but the old lock mechanism was massive. So I have to find a way of filling in that area so I can drill the correct holes and paint(will not be staining).

What is my best option? I wouldn't think wood filler would work because it's too soft. I've heard Bondo works which I know is a little ghetto but I will be standing and painting over it.